The present invention relates to an optical transmission apparatus, and more particularly to a wideband optical receiving apparatus or an optical receiving module for converting a digital optical signal into an electric signal and a technique particularly effective in utilizing for improvement of frequency characteristics thereof.
Development of a wideband optical receiving apparatus or an optical receiving module is being proceeded as an optical transmission apparatus for converting a digital optical signal exceeding several GHz into an electric signal. Since the characteristic required for the wideband optical receiving apparatus or the optical receiving module is the application of a wideband signal in which the frequency of an optical signal has frequency components from a frequency close to a direct current to a frequency close to a transmission bit rate, it has been found that it will become important to form the frequency characteristics of various semiconductor integrated circuits or various amplification circuits to be used in the wideband optical receiving apparatus or the optical receiving module.
A wideband feedback amplification circuit which includes bipolar transistors (hereinafter referred to simply as transistors) as a basic element and can correspond to a high frequency signal at the level of several GHz is stated in, for example, "IEEE (Institute of Electrical and Electronics Engineers) Journal of Solid-State Circuits Vol. 24, No. 6" for December, 1989, pp. 1744-1748.
As shown in FIG. 7, the feedback amplification circuit described above is provided with a transadmittance type amplification circuit and a transimpedance type amplification circuit. The transadmittance type amplification circuit includes a pair of transistors T41 and T42 of differential configurations having bases for receiving an inverted input signal VInB and a non-inverted input signal VInT which are formed as voltage signals, respectively. Similarly, the transimpedance type amplification circuit includes a pair of transistors T11 and T12 of differential configurations coupled with collectors of transistors T41 and T42, respectively. Feedback resistances RF11 and RF12 are provided between the collectors and the bases of the transistors T11 and T12, respectively. Further, collector potentials of the transistors T11 and T12 become an inverted output signal OutB and a non-inverted output signal OutT that are voltage signals of a feedback amplification circuit after going through an emitter follower circuit having a two-step construction including transistors T5 and T6 or T7 and T8, respectively. What is called peaking capacity C1 is provided substantially in parallel with emitter resistances R41 and R42 between the emitters of the transistors T41 and T42. With this, it is aimed to enlarge the bandwidth in a high frequency area of the feedback amplification circuit.
On the other hand, in a feedback amplification circuit shown in FIG. 7, the frequency characteristics of the transimpedance type amplification circuit which is liable to produce band deterioration produces a great influence upon the frequency characteristics of the whole feedback amplification circuit. Further, in this transimpedance type amplification circuit, the feedback resistances RF11 and RF12 form a single feedback loop (a feedback path) making a feedback gain thereof to be .beta.0 and phase delay to be .phi.0 as shown in FIG. 8 with respect to an open loop type amplifier A composed of the transistor T11 or T12. Furthermore, according to "Analysis and Design of Analog Integrated Circuits" p.117 under joint authorship with P. R. Gray and R. G. Meyor and under supervision of Yuzuru Nagata published by Baifukan, a feedback amplification circuit has the most flat and wideband frequency characteristics when a phase margin at a point where the loop gain becomes 1, in a word, a value obtained by subtracting the phase delay .phi.0 of the feedback loop from 180 degrees is set to 60 degrees.